The present invention relates to a semiconductor device, a battery pack, and a personal data assistant, and particularly relates to a technique effective in case that applied to a semiconductor device for monitoring the state of a battery.
In recent years, CPUs (including a GPU) mounted on an internal circuit (PC system) in a personal data assistant such as a notebook computer have had a gradual tendency to be provided with a variable frequency function in order to have a balance between power consumption, arithmetic operation performance and reliability (lifetime). The variable frequency function means that during a normal time, power consumption is reduced by setting the clock frequency of the CPU to be relatively low (normal clock operation) and a deterioration in the reliability of the CPU is suppressed by suppressing a temperature rise of the CPU, and that during an increase in a CPU resource request of an application, arithmetic operation performance is improved by setting the clock frequency of the CPU to be high (high-speed clock operation).
In case that an AC adapter is not connected to a notebook computer during a CPU's high-speed clock operation, the entire power required for a CPU's high-speed clock operation is supplied from a battery (assembled battery obtained by combining a plurality of secondary battery cells). On the other hand, in case that an AC adapter is connected to a notebook computer, power required for a high-speed clock operation is supplied from the AC adapter and the battery. This is because a maximum power of the AC adapter is designed to be smaller than a maximum power required during a high-speed clock operation for the purpose of a reduction in weight, a reduction in power consumption, and a reduction in cost. Meanwhile, power drawn from the battery as shortage power of the AC adapter during a high-speed clock operation is supplemented by the battery being charged through the AC adapter during a normal clock operation.
As stated above, in order for the CPU to perform a high-speed clock operation, a supply of power from the battery is required regardless of the presence or absence of the connection of the AC adapter. For this reason, a period in which the CPU performs a high-speed clock operation and a clock frequency during a high-speed clock operation are determined on the basis of the amount of power which is capable of being supplied from the battery. For example, the CPU having a variable frequency function is configured such that a plurality of clock frequencies higher than a clock frequency during a normal clock operation can be selected as a clock frequency during a high-speed clock operation, and an optimum clock frequency is selected in accordance with the amount of power which is capable of being supplied from the battery in that case.
On the other hand, the state of the battery mounted on a personal data assistant such as a notebook computer is monitored by a battery monitoring system mounted on a battery pack together with the battery. Generally, the battery monitoring system is configured to include a battery control IC (FGIC: Fuel Gauge IC), a sense resistor for detecting charging and discharging currents of the battery as voltage information, a charge control MOS transistor, a discharge control MOS transistor, and a protective circuit such as a thermistor or a fuse. The battery control IC is configured to include, for example, a microcontroller, and realizes a function of managing the remaining capacity of a battery, a function of controlling a charge control/discharge control MOS transistor, a function of protecting a battery, and the like. For example, the battery control IC generates information indicating a battery state on the basis of detection results of charging and discharging currents and a battery voltage of a battery, and notifies an internal circuit of a personal data assistant of the information. The information indicating a battery state includes, for example, full charge capacity (FCC), Remaining Capacity (RC) of abattery, state of charge (SOC) of a battery, and the like. A conventional example of the battery control IC is disclosed in, for example, JP-A-2010-34016, JP-A-2003-79059, and JP-A-2001-51029.
In the battery control IC mounted on a battery pack of a notebook computer on which the CPU having the aforementioned variable frequency function is mounted, information of the amount of maximum power which is capable of being supplied from the battery to the internal circuit is generated on the basis of measurement results of a discharging current and a battery voltage of the battery, in addition to the information indicating the battery state mentioned above. The information of the amount of maximum power is notified to a PC system (internal circuit) of a notebook computer at any time (for example, once per second), and is used, as described above, in determining a clock frequency during the high-speed clock operation or a period of the high-speed clock operation.